1. Field of the Invention
The present invention relates to a network monitoring device disposed at a node connected to a network, capable of monitoring the status condition of a connection between at least another node and the network.
2. Description of the Prior Art
Referring now to FIG. 12, there is illustrated a block diagram showing the structure of a prior art network monitoring system as disclosed in for, for example, Japanese Patent Application Laying Open (KOKAI) No. 2-125361. In the figure, reference numeral 1 denotes a network, A1 to An denote host computers, each of which will be referred to as a CPU and each of which is connected to the network 1, B1 to Bn denote storage devices connected to the plurality of CPUS A1 to An, respectively, C1 to Cm denote terminal control devices each of which is connected to two or more CPUS, for controlling communications between the CPUs and some terminals, and D1 to Dk, E1 to Ek, and F1 to Fk denote terminals.
Each of the plurality of CPUs A1 to An includes a time measurement unit for measuring the time of arrival of a monitoring message from another CPU, indicating that the other CPU is running, in order to monitor the operating condition of the other CPU and the status of a connection between the other CPU and the network 1, and a determination unit for determining whether the monitoring message has arrived within a predetermined period of time.
To be more specific, instead of making only one CPU perform centralized management of the operating conditions and so on of the other CPUS, each of the plurality of CPUs A1 to An is allowed to broadcast a monitoring message on the network 1 and gather monitoring messages sent by the other CPUs by its own efforts to check their operating conditions. Each of the plurality of CPUs A1 to An can send a monitoring message at predetermined intervals as long as it is running. Each monitoring message is given an identifier indicating the sender.
For example, assume that the CPU An malfunctions as shown in FIG. 13 and therefore cannot send a monitoring message while the other CPUs A1 and A2 can send a monitoring message. Each of those CPUs can measure the time of arrival of a monitoring message (e.g. CCA-A) from the other CPUs and store the measured time in its storage device. Then, each of the CPUs A1 and A2 can determine that the other CPU An malfunctions because it does not receive a monitoring message from the other CPU An for a predetermined period of time or more.
A problem with such a prior art network monitoring device which is so constructed as mentioned above is that while each of the CPUs within the network can recognize the occurrence of a malfunction in another CPU unless it receives a monitoring message from the other CPU within a predetermined period of time, each of the CPUs needs to increase the length of its monitoring intervals at which it monitors the other CPUs with an increase in the number of CPUs connected to the network 1 because this results in increasing the amount of communication processing in each of all the CPUs, thereby interfering with other communication processing. Another problem is that since each of the CPUs has to periodically broadcast a monitoring message to the other CPUS, it is difficult to apply the prior art network monitoring system to a high-speed switching-type network such as an ATM or Ethernet Switch and there is a limit on the physical topology of the network.
To reduce the amount of communication processing in each of the CPUs connected to the network and apply the prior art network monitoring system to a high-speed switching-type network, each of the CPUs can simply perform a unicast mutual monitoring operation by monitoring a specified CPU. However, if there is provided a server or a manager for centralized-monitoring all the CPUs, a malfunction in the server or the like can cause a malfunction in the whole of the network.
The present invention is made to overcome the above problems. It is therefore an object of the present invention to provide a network monitoring device capable of decreasing the length of its monitoring intervals at which it monitors at least another CPU or node within a network without an increase in the amount of communication processing in each of the CPUs within the network, thereby expanding its applicability to high-speed switching-type networks.
In accordance with one aspect of the present invention, there is provided a network monitoring device disposed at a node connected to a network, comprising: a response unit, responsive to a monitoring packet from a neighboring node downstream, for sending a response packet to the neighboring node downstream; a determination unit for sending a monitoring packet to a neighboring node upstream, and for determining that the neighboring node upstream has broken away from the network unless the determination unit does not receive a response packet responsive to the monitoring packet from the neighboring node upstream; and a notification unit for, when that the determination unit has determined that the neighboring node upstream has broken away from the network, broadcasting a notification packet indicating the event to all other nodes connected to the network.
In accordance with another aspect of the present invention, there is provided a network monitoring device disposed at a node connected to a network, comprising: a response unit, responsive to a monitoring packet from a neighboring node either upstream or downstream, for sending a response packet to the neighboring node either upstream or downstream; a determination unit for sending a monitoring packet to a neighboring node downstream, and for determining that the neighboring node downstream has broken away from the network unless the determination unit does not receive a response packet responsive to the monitoring packet from the neighboring node downstream; and a notification unit for, when that the determination unit has determined that the neighboring node downstream has broken away from the network, broadcasting a notification packet indicating the event to all other nodes connected to the network.
In accordance with a preferred embodiment of the present invention, the network monitoring device further comprises a management table for storing logical addresses identifying the neighboring nodes upstream and downstream, respectively, and a updating unit for updating the management table when the determination unit has determined that the neighboring node either upstream or downstream has broken away from the network or upon receipt of a notification packet indicating that another node has broken away the network.
In accordance with another preferred embodiment of the present invention, when the node to which the network monitoring device belongs newly participates in the network, the updating unit broadcasts a monitoring packet to all other nodes connected to the network and generates the management table based on response packets responsive to the monitoring packet, which can be sent by the all other nodes.
In accordance with another preferred embodiment of the present invention, in response to a monitoring packet from another node that has newly participated in the network, the response unit sends a response packet responsive to the monitoring packet to the other node and the updating unit updates the management table.
In accordance with another preferred embodiment of the present invention, the determination unit sends a monitoring packet to at least another node disposed between the node to which the network monitoring device belongs to and the neighboring node either upstream or downstream, which has not participated in the network yet.
In accordance with another preferred embodiment of the present invention, when there are a predetermined or more number of other nodes that lie between the node to which the network monitoring device belongs to and the neighboring node either upstream or downstream and that have not participated in the network yet, the determination unit broadcasts a monitoring packet to the other nodes that have not participated in the network yet.
In accordance with another preferred embodiment of the present invention, the network monitoring device further comprises a searching unit for, when the determination unit has determined that the neighboring node either upstream or downstream has broken away from the network, sending a monitoring packet to one or more other nodes that belong to a search area either upstream or downstream, and for searching for a new neighboring node either upstream or downstream based on one or more packets responsive to the monitoring packet.
In accordance with another preferred embodiment of the present invention, unless the searching unit is able to find out the new neighboring node either upstream or downstream through the search area, it changes and shifts the search area including one or more other nodes in an either upstream or downstream direction, and then sends a monitoring packet to the search area again.
In accordance with another preferred embodiment of the present invention, the network monitoring further comprises a numbering unit for adding a time-sequence number to any packet to be sent to another node.
In accordance with another preferred embodiment of the present invention, when the updating unit needs to update the management table using a packet applied thereto from another node, it refers to a time-sequence number added to the packet, and then updates the management table only if the received packet is associated with the latest event that occurred in the other node.
In accordance with another preferred embodiment of the present invention, the network monitoring device further comprises an event sending unit for sending a message indicating the occurrence of an event to a corresponding queue already registered when it is determined on the network that another node has participated in the network or broken away from the network.
In accordance with another preferred embodiment of the present invention, the network monitoring device further comprises one or more other determination units whose operating intervals are different from each other and that of the first determination unit, and one or more other notification units whose operating intervals are different from each other and that of the first notification unit.